David Kramer’s article on nuclear developments in my native Canada (Physics Today, January 2021, page 23) was an enjoyable read. However, his assertion that the Zero Energy Experimental Pile (ZEEP) world’s second operating reactor after Enrico Fermi’s Chicago Pile-1 (CP-1) is erroneous; at least nine other stateside piles achieved criticality before ZEEP did so September 1945.Those US were CP-2...